Added FundMe & PriceConverter

contracts/FundMe.sol

@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.8;
+
+import "@chainlink/contracts/src/v0.8/shared/interfaces/AggregatorV3Interface.sol";
+import "./PriceConverter.sol";
+
+error NotOwner();
+
+contract FundMe {
+    using PriceConverter for uint256;
+
+    mapping(address => uint256) public addressToAmountFunded;
+    address[] public funders;
+
+    // Could we make this constant?  /* hint: no! We should make it immutable! */
+    address public /* immutable */ i_owner;
+    uint256 public constant MINIMUM_USD = 50 * 10 ** 18;
+    
+    constructor() {
+        i_owner = msg.sender;
+    }
+
+    function fund() public payable {
+        require(msg.value.getConversionRate() >= MINIMUM_USD, "You need to spend more ETH!");
+        // require(PriceConverter.getConversionRate(msg.value) >= MINIMUM_USD, "You need to spend more ETH!");
+        addressToAmountFunded[msg.sender] += msg.value;
+        funders.push(msg.sender);
+    }
+    
+    function getVersion() public view returns (uint256){
+        // ETH/USD price feed address of Sepolia Network.
+        AggregatorV3Interface priceFeed = AggregatorV3Interface(0x694AA1769357215DE4FAC081bf1f309aDC325306);
+        return priceFeed.version();
+    }
+    
+    modifier onlyOwner {
+        // require(msg.sender == owner);
+        if (msg.sender != i_owner) revert NotOwner();
+        _;
+    }
+    
+    function withdraw() public onlyOwner {
+        for (uint256 funderIndex=0; funderIndex < funders.length; funderIndex++){
+            address funder = funders[funderIndex];
+            addressToAmountFunded[funder] = 0;
+        }
+        funders = new address[](0);
+        // // transfer
+        // payable(msg.sender).transfer(address(this).balance);
+        // // send
+        // bool sendSuccess = payable(msg.sender).send(address(this).balance);
+        // require(sendSuccess, "Send failed");
+        // call
+        (bool callSuccess, ) = payable(msg.sender).call{value: address(this).balance}("");
+        require(callSuccess, "Call failed");
+    }
+    // Explainer from: https://solidity-by-example.org/fallback/
+    // Ether is sent to contract
+    //      is msg.data empty?
+    //          /   \ 
+    //         yes  no
+    //         /     \
+    //    receive()?  fallback() 
+    //     /   \ 
+    //   yes   no
+    //  /        \
+    //receive()  fallback()
+
+    fallback() external payable {
+        fund();
+    }
+
+    receive() external payable {
+        fund();
+    }
+
+}
+
+// Concepts we didn't cover yet (will cover in later sections)
+// 1. Enum
+// 2. Events
+// 3. Try / Catch
+// 4. Function Selector
+// 5. abi.encode / decode
+// 6. Hash with keccak256
+// 7. Yul / Assembly

contracts/PriceConverter.sol

@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.8;
+
+import "@chainlink/contracts/src/v0.8/shared/interfaces/AggregatorV3Interface.sol";
+
+// Why is this a library and not abstract?
+// Why not an interface?
+library PriceConverter {
+    // We could make this public, but then we'd have to deploy it
+    function getPrice() internal view returns (uint256) {
+        // Sepolia ETH / USD Address
+        // https://docs.chain.link/data-feeds/price-feeds/addresses#Sepolia%20Testnet
+        AggregatorV3Interface priceFeed = AggregatorV3Interface(
+            0x694AA1769357215DE4FAC081bf1f309aDC325306
+        );
+        (, int256 answer, , , ) = priceFeed.latestRoundData();
+        // ETH/USD rate in 18 digit
+        return uint256(answer * 10000000000);
+        // or (Both will do the same thing)
+        // return uint256(answer * 1e10); // 1* 10 ** 10 == 10000000000
+    }
+
+    // 1000000000
+    function getConversionRate(
+        uint256 ethAmount
+    ) internal view returns (uint256) {
+        uint256 ethPrice = getPrice();
+        uint256 ethAmountInUsd = (ethPrice * ethAmount) / 1000000000000000000;
+        // or (Both will do the same thing)
+        // uint256 ethAmountInUsd = (ethPrice * ethAmount) / 1e18; // 1 * 10 ** 18 == 1000000000000000000
+        // the actual ETH/USD conversion rate, after adjusting the extra 0s.
+        return ethAmountInUsd;
+    }
+}

contracts/SimpleStorage.sol

@@ -5,10 +5,10 @@ contract SimpleStorage {
     // boolean, uint, int, address, bytes
     address public myAddress = 0xc9445E993dAeA4bA3F1FE1080F0F6f8c46b4d967;
     uint256 public myNumber = 123; // With Getter, Retrieval Need Gas
-    string myText = "Hello World";
+    string private myText = "Hello World";
     //int256 favoriteInt = -5;
     //bytes32 favoriteBytes = "cat";
-    uint256 myDefaultZero; // Initialize default to 0
+    uint256 private myDefaultZero; // Initialize default to 0
 
     // Paid
     function storeMyNumber(uint256 _favoriteNumber) public virtual {